Scala - copy case class with dynamic fields. Is it possible?

Question

Considering a case class that has a default field calculated at creating time, is it possible to copy it where the new copied case class has this field recalculated?

For example, TestCopy.auto is generated at creation time:

  case class TestCopy(static: String, auto: Long = System.currentTimeMillis()) {
    val auto2 = System.currentTimeMillis()
  }

If I copy it changing only the field static:

    val a = TestCopy(static = "a")
    val b = a.copy(static = "b")

The field auto is not recalculated. Neither is the constructor field auto2:

> println(a)
> println(b)
> println(a.auto2)
> println(b.auto2)

TestCopy(a,1640773176392)
TestCopy(b,1640773176392)
1640773176392
1640773176392

It makes sense, actually, since I am copying the case class. However, I wanted a behaviour similar to recreating the case class, where I change only a set of static fields. The example above is simplified, I could have just created it again. The question is aiming at cases like:

  case class TestCopy2(static1: String,
                       static2: String,
                       static3: String,
                       auto: Long = System.currentTimeMillis())

Where only static1 must be changed, static2 and static3 must be copied, and auto must be generated again. Is it possible?

Thank you all.

Answer 1

Transient values don't get copied automatically:

case class Foo(a: Int) { 
   @transient val b: Long = System.currentTimeMillis 
}


val f1 = Foo(1)
Thread.sleep(1000)
val f2 = f1.copy(2)

assert f1.b != f2.b